Conventional silent chain transmission devices include a silent chain transmission device as shown in Japanese laid-open Patent Publication No. Hei. 8-184348. In that device, inside flank surfaces in each row of the chain, when stretched linearly, take the form of a portion of the tooth shape of a rack cutter capable of cutting the teeth of the sprocket which meshes with the chain. By forming the tooth surfaces of the sprocket using a rack cutter having a sectional shape corresponding to that of the inside flank surfaces in the contiguous link plates when the silent chain is stretched linearly, polygonal motion of the chain is decreased, and noise is thereby reduced.
When the link plates of the silent chain begin to engage with the sprocket, since the inside flank surfaces of the respective link plates enter from a tangential direction in the same manner as the sectional shape of the rack cutter, polygonal motion of the chain is avoided because the chain and sprocket operate in the same manner as a rack and pinion mechanism. However, when a link plate of the silent chain seats on the sprocket while engaging with and wrapping around the sprocket, polygonal motion of the chain occurs as in conventional silent chains. Thus, polygonal motion of the chain cannot be completely avoided in the process of engagement of the silent chain with the sprocket. Therefore, the problems of vibration, noise and tension variation in the silent chain transmission device could not be solved completely.
There was also the problem that the inwardly curved portion contiguous with and connecting the inside flank surfaces of a link plate interfered with the tooth heads of the sprocket, and the problem that the heads of the V-shaped link teeth interfered with the bottoms of the gaps between the sprocket teeth. Consequently, wear, biased wear, missing teeth, and the like, occurred in the inwardly curved portions of the link plates, the tooth head portions of the V-shaped link teeth, and the bottoms of the tooth gaps of the sprocket.
A proposed silent chain transmission device was disclosed in Japanese patent No. 3108417. In that device as shown in FIG. 6, to reduce vibration noise, changes in chain tension due to polygonal motion of the chain, and wear loss in the tooth heads of the link plates and the tooth gap bottoms of the sprocket, an inward curved portion A11c of the link plate A11 is recessed to a position where contact interference with the tooth heads of the sprocket A20, due to the amplitude of the polygonal motion of the chain, is avoided, when the outside engaging surfaces A11b of a link plate A11 are engaged with a sprocket A20 and seated thereon.
In the silent chain transmission device disclosed in the specification of Japanese patent number 3108414, however, as shown in FIG. 7, the inward curved portion of the link plate A11 is recessed and in the form of a portion of a circular bore. Unnatural engagement between the inside engaging surface of the link plate A11 and the tooth gap of the sprocket A20 occurs in the process of advancing engagement of the link plate A11 with the sprocket, and wrapping of the chain around the sprocket, as shown in FIG. 6. The unnatural engagement produces stress concentration, friction, and the like. Thus, sufficient reduction in noise, and durability of the silent chain transmission device were not achieved.
Furthermore, since the inwardly curved portion A11c of the link plate A11 is recessed, its margin is intersected by the opposed, diverging, inside sprocket-engaging surfaces A11a. Consequently, the lengths of the inside sprocket-engaging surfaces A11a are insufficient to ensure a rapid shift from inside engagement to outside engagement. Thus, there were not only the problems of insufficient noise reduction and insufficient durability, but also the problem of insufficient fatigue strength in the silent chain.
In a silent chain, a slight shift exists in the positions of the bores for receiving connecting pins A12, due to vibration during the punching process. Even if the link plate A11 is punched precisely, the respective portions in the link plate A11 do not always exhibit left-to-right symmetry. That is, dimension A and B are different from each other, as are dimensions C and D (A≠B, C≠D) Unlike the link plate shown in FIG. 8(c), where A=B and C=D, the dimensions may be related as shown in FIG. 8(a), where A>B and C<D. Thus, when a number of link plates A11 are collected at random, and arranged in parallel to each other to form a widthwise link row A10a, the inside diverging surfaces of the link row, which correspond to an envelope of the widthwise projections of all the inside diverging surfaces in a row, are spaced by a distance w, which, as shown in FIG. 8(b), is slightly smaller than corresponding distance W in the individual link plates A11. As a result, the engagement between the silent chain A10 and the sprocket A20 became tight, engagement failure occurred, further vibration, noise, and engagement interference were generated at the engaging surfaces of the silent chain A10 and the sprocket A20, and wear resistance was significantly reduced.
Accordingly, an object of this invention is to provide a silent chain transmission device in which the engagement time of the inside engaging surfaces is controlled, so that vibration noise and impact noise are decreased, and stress concentration and wear at the inside engaging surfaces and inside inward curved portions of the link plates, and the tooth head portions of the sprocket, are prevented. Other objects of the invention are to improve the durability of the chain, and to reduce the burden of ensuring accuracy in the production of the chain components and in the assembly of the silent chain.